Peptidoglycan, as well as lipopolysaccharide (LPS), is a surface component of many bacteria, which elicits a wide range of physiological and immune responses in humans. Specifically, peptidoglycan has been shown to manifest itself clinically by reproducing most of the symptoms of bacterial infection, including fever, acute-phase response, inflammation, septic shock, leukocytosis, sleepiness, malaise, abscess formation, and arthritis (see Dziarski et al., JBC, 273 (15): 8680 (1998)). Furthermore, the type of peptidoglycan (i.e.—the specific stereoisomers or analogs of muramyl dipeptide, N-acetylglucosaminyl-beta(1-4)-N-acteylmuramyl tetrapeptides, etc.), were shown to elicit a broad range of activities, including exhibiting greater pyrogenicity, inducing acute joint inflammation, stimulating macrophages, and causing hemorrhagic necrosis at a primed site (See Kotani et al., Fed Proc, 45(11): 2534 (1986)).
It has been demonstrated in humans that a lipopolysaccharide binding protein exists that was discovered as a trace plasma protein (See Schumann et al., Science, 249(4975):1429 (1990)). It is thought that one of the modes of action by which this lipopolysaccharide binding protein functions is by forming high-affinity complexes with lipopolysaccharide, that then bind to macrophages and monocytes, inducing the secretion of tumor necrosis factor. Dziarski and Gupta (See Dziarski et al., JBC, 269(3): 2100 (1994)) demonstrated that a 70 kDa receptor protein present on the surface of mouse lymphocytes served to bind heparin, heparinoids, bacterial lipoteichoic acids, peptidoglycan, and lipopolysaccharides.
Recently, Dziarski et al. demonstrated that the CD14, a glycosylphosphatidylinositol-linked protein present on the surface of macrophage and polymorphonuclear leukocytes, bound peptidoglycan and lipopolysaccharide. Furthermore, the binding affinity of CD14 for lipopolysaccharide was significantly increased in the presence of a LPS-binding protein present in plasma. It is thought that the LPS-binding protein functions as a transfer molecule, whereby it binds LPS and presents it to the CD14 receptor (See Dziarski et al., JBC, 273(15): 8680 (1998)).
Yoshida et al. isolated a peptidoglycan binding protein from the hemolymph of the Silkworm, Bombyx mori, using column chromatography. This protein was found to have a very specific affinity for peptidoglycan (See Yoshida et al., JBC, 271(23): 13854 (1996)). Additionally, Kang et al. recently cloned a peptidoglycan binding protein from the moth Trichoplusia ni. The peptidoglycan binding protein was shown to bind strongly to insoluble peptidoglycan (See Kang et al., PNAS, 95(17): 10078 (1998)). In this study the peptidoglycan binding protein was upregulated by a bacterial infection in T. ni. The insect immune system is regarded as a model for innate immunity. Thus, Kang et al were able to clone both mouse and human homologs of the T. ni peptidoglycan binding protein. All of these peptidoglycan binding proteins shared regions of homology, as well as four conserved cysteine residues which may function in the tertiary structure of the protein, possibly in helping to form binding domains. Given that peptidoglycan is an integral component of bacterial cell walls, and that it induces many physiological responses from cytokine secretion to inflammation and macrophage activation, it appears as if this family of proteins may be a ubiquitous group involved in the binding and recognition of peptidoglycan, the presentation of antigens (e.g., cell wall components, etc.), and the activation of the immune system, such as the secretion of cytokines, such as TNF.
TNF is noted for its pro-inflammatory actions which result in tissue injury, such as induction of procoagulant activity on vascular endothelial cells (Pober, J. S. et al., J. Immunol. 136:1680 (1986)), increased adherence of neutrophils and lymphocytes (Pober, J. S. et al., J. Immunol. 138:3319 (1987)), and stimulation of the release of platelet activating factor from macrophages, neutrophils and vascular endothelial cells (Camussi, G. et al., J. Exp. Med. 166:1390 (1987)).
Recent evidence implicates TNF in the pathogenesis of many infections (Cerami, A. et al., Immunol. Today 9:28 (1988)), immune disorders, neoplastic pathology, e.g., in cachexia accompanying some malignancies (Oliff, A. et al., Cell 50:555 (1987)), and in autoimmune pathologies and graft-versus host pathology (Piguet, P.-F. et al., J. Exp. Med. 166:1280 (1987)). The association of TNF with cancer and infectious pathologies is often related to the host's catabolic state. A major problem in cancer patients is weight loss, usually associated with anorexia. The extensive wasting which results is known as “cachexia” (Kern, K. A. et al J. Parent. Enter. Nutr. 12:286-298 (1988)). Cachexia includes progressive weight loss, anorexia, and persistent erosion of body mass in response to a malignant growth. The cachectic state is thus associated with significant morbidity and is responsible for the majority of cancer mortality. A number of studies have suggested that TNF is an important mediator of the cachexia in cancer, infectious pathology, and in other catabolic states.
TNF is thought to play a central role in the pathophysiological consequences of Gram-negative sepsis and endotoxic shock (Michie, H. R. et al., Br. J. Surg. 76:670-671 (1989); Debets, J. M. H. et al., Second Vienna Shock Forum, p.463-466 (1989); Simpson, S. Q. et al., Crit. Care Clin. 5:27-47 (1989)), including fever, malaise, anorexia, and cachexia. Endotoxin is a potent monocyte/macrophage activator, which stimulates production and secretion of TNF (Kombluth, S. K. et al., J. Immunol. 137:2585-2591 (1986)) and other cytokines. Because TNF could mimic many biological effects of endotoxin, it was concluded to be a central mediator responsible for the clinical manifestations of endotoxin-related illness. TNF and other monocyte-derived cytokines mediate the metabolic, neurological and hormonal responses to endotoxin (Michie, H. R. et al., N. Eng. J. Med. 318:1481-1486 (1988)). Endotoxin administration to human volunteers produces acute illness with flu-like symptoms including fever, tachycardia, increased metabolic rate and stress hormone release (Revhaug, A. et al., Arch. Surg. 123:162-170 (1988)). Elevated levels of circulating TNF have also been found in patients suffering from Gram-negative sepsis (Waage, A. et al., Lancet 1:355-357 (1987); Hammerle, A. F. et al., Second Vienna Shock Forum p. 715-718 (1989); Debets, J. M. H. et al., Crit. Care Med. 17:489-497 (1989); Calandra, T. et al., J. Infec. Dis. 161:982-987 (1990)).
Passive immunotherapy directed at neutralizing TNF may have a beneficial effect in Gram-negative sepsis and endotoxemia, based on the increased TNF production and elevated TNF levels in these pathology states, as discussed above. Antibodies to a “modulator” material which was characterized as cachectin (later found to be identical to TNF) were disclosed by Cerami et al. (EPO Patent Publication 0,212,489, Mar. 4, 1987). Such antibodies were said to be useful in diagnostic immunoassays and in therapy of shock in bacterial infections. Rubin et al. (EPO Patent Publication 0,218,868, Apr. 22, 1987) disclosed monoclonal antibodies to human TNF, the hybridomas secreting such antibodies, methods of producing such antibodies, and the use of such antibodies in immunoassay of TNF. Yone et al. (EPO Patent Publication 0,288,088, Oct. 26, 1988) disclosed anti-TNF antibodies, including mAbs, and their utility in immunoassay diagnosis of pathologies, in particular Kawasaki's pathology and bacterial infection. The body fluids of patients with Kawasaki's pathology (infantile acute febrile mucocutaneous lymph node syndrome; Kawasaki, T., Allergy 16:178 (1967); Kawasaki, T., Shonica (Pediatrics) 26:935 (1985)) were said to contain elevated TNF levels, which were related to progress of the pathology (Yone et al., supra).
Kiselev et al. isolated tag7, which is a secreted murine cytokine with remote homology to the TNF family of ligands (Kiselev, S. L., et al, J. Biol. Chem., 273:18633-39 (1998)). It was found that tag7 triggers apoptosis in murine L929 cells in vitro, and thus may be a molecule that possesses significant cytotoxicity in vivo that is realized through apoptosis. Furthermore, tag7 is expressed constitutively in hematopoietic and lymphoid tissues, suggesting that it may play a role in normal immune system function.
Accordingly, there is a need to provide molecules that are involved in pathological conditions. Such novel proteins could be useful in augmenting the immune system in such areas as immune recognition, antigen presentation, and immune system activation. Antibodies or antagonists directed against these proteins may be useful in reducing or eliminating disorders associated with TNF and TNF-like cytokines, such as endotoxic shock and auto-immune disorders, for example.